Re: [PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable hstates

[Mike Kravetz]

On 1/28/21 1:37 PM, Andrew Morton wrote:
> On Thu, 28 Jan 2021 06:52:21 +0100 Oscar Salvador <osalvador@xxxxxxx> wrote:
> 
>> On Wed, Jan 27, 2021 at 03:36:41PM -0800, Mike Kravetz wrote:
>>> Yes, this patch is somewhat optional.  It should be a minor improvement
>>> in cases where we are dealing with hpages in a non-migratable hstate.
>>> Although, I do not believe this is the common case.
>>>
>>> The real reason for even looking into this was a comment by Oscar.  With
>>> the name change to HPageMigratable, it implies that the page is migratable.
>>> However, this is not the case if the page's hstate does not support migration.
>>> So, if we check the hstate when setting the flag we can eliminate those
>>> cases where the page is certainly not migratable.
>>>
>>> I don't really love this patch.  It has minimal functional value.
>>>
>>> Oscar, what do you think about dropping this?
>>
>> Yeah, I remember this topic arose during a discussion of patch#2 in the
>> early versions, about whether the renaming to HPageMigratable made
>> sense.
>>
>> Back then I thought that we could have this in one place at fault-path [1],
>> which should have made this prettier, but it is not the case.
>> True is that the optimization is little, so I am fine with dropping this
>> patch.
> 
> I've dropped it.

Thanks Andrew.

Michal suggested that comments describing synchronization be added for each
flag.  Since I did 'one patch per flag', that would be an update to each patch.
Or, I could simply add a patch to update the comment block based on what you
already have.

Let me know what is best/easiest for you.
-- 
Mike Kravetz